Users of fixed line terminals or mobile stations (such as a mobile telephone or a transceiver unit provided with data processing capabilities or a transceiver unit provided with capability of using TCP/IP protocol (Transport Control Protocol/Internet Protocol) suite or similar user equipment) may want to switch from one operator providing an original subscription to another operator without having to change the number or address of the subscription. This kind of possibility would strengthen the user's position with respect to the operators and facilitate the user making use of the most generous offers by different operators and/or to use operators which give the best value for money and/or best service at any moment.
Mobile users have the possibility to utilise the so called mobile number portability (MNP) feature for the above. A more detailed description of one possibility for the MNP can be found e.g. from the ETSI MNP (European Telecommunications Standards Institute—Mobile Number Portability) specification. In general, the MNP allows the number of a mobile subscriber to remain unchanged when the network or the operator is changed i.e. ported from one operator to another. This means that within the MNP the mobile subscriber is able to change the subscription network within the same country while retaining his or her original MSISDN (Mobile Subscriber ISDN number) or several MSISDNs. In principle it is also possible to change from an operator in one country to an operator in another country, but there may be some international/national legislation and regulations which may prevent porting between different countries.
A mobile user (or subscriber) having used the MNP assignment is sometimes referred to as an exported or ported mobile user. Calls to the ported mobile user are, depending in most cases on national requirements, first routed to the original network of the user on the basis of the unchanged mobile number (i.e. on the basis of the MSISDN of the user). Then a specific routing register located in the old network recognises that the number is an exported number, and subsequently redirects the call related signalling to the new recipient network. The call is then routed to the called mobile subscriber by means of the routing arrangement of the new network. The MNP implementations can also route short messages (e.g. GSM SMS messages) and other non-call related signalling.
As mentioned above, special routing registers or databases have been implemented into the telecommunications networks in order to enable the operation of the number portability service, the registers containing necessary rerouting information of the ported mobile subscribers. In one network, all affected non-call related signalling messages and routing enquiry messages originated in the respective network or outside the network can be routed through the routing register (or several registers). The routing register may provide e.g. the following functions:                Relay of E.164 addressed SCCP (Signalling Connection Control Part) messages directed to the network's own subscriber to the correct HRL (Home Location Register: a register in the subscribed network containing information associated to the subscriber); and        Relay of routing enquiry messages addressed to, for example, a ported subscriber and served by another network to the MAP (Mobile Application Part) level NP (Number Portability) application. The NP application returns the routing number in MAP SRI (Send Routing Information) response message. The routing number then enables routing of the call to the recipient network for call handling.        
A MAP based NP database query can be used for the required call related functionality. The specific routing register is used for identifying the ported status of the addressed MSISDN in conjunction with a MAP level application to provide necessary re-routing information in a MAP SRI response message.
Thus the routing register functionality has a key role in a telecommunications system providing mobile number portability. The main functionality of the routing register is to provide operators with rerouting capability and an application level functionality for returning the required routing information. The routing register handles both non-call and call related signalling messages. By means of the routing register the subscriber is able to keep the existing mobile telephone number when porting from one operator to the new one. The rerouting functionality is achieved with the free association of the “phone number routing information” (the subscriber phone number can be, for instance, the MSISDN). The routing information can be a real directory number for a service number, an address of a network element or, for instance, a mobile number portability routing number inquired from an internal database of the routing register.
In principle the ported subscriber should be able to use exactly the same services as a non-ported subscriber in the same subscription network. In other words, in order to receive the maximum benefit of the number portability service there should be no difference in whether the subscriber's MSISDN belongs to the used network or whether the subscriber's MSISDN is ported to the used network—the services offered to the user by that subscription network and the service level should nevertheless be the same.
These services offered to the users include supplementary telecommunication services or functionalities. The supplementary services are also sometimes referred to as intelligent network (IN) services or advanced telecommunications services. The supplementary or intelligent network service can be defined as a telecommunication feature providing various sophisticated services or value-added services to the subscribers, for instance by means of software and/or hardware implementations provided in one or several nodes of the telecommunications system. The user can access the supplementary telecommunications services by means of his terminal, either fixed or mobile. The supplementary network service comprises an ever increasing amount of services such as prepaid calls, differently priced calls to different numbers or number spaces, call blocking (“do not disturb”) or barring of calls from certain numbers or number spaces, call forwarding, callback (completion of call to a busy/unreachable subscriber), remote control of services, calls for various toll free numbers (“freephone”) or specially priced numbers, answering/voice mail, conference calls or group calls, announcements to the users, such as calling number information or remaining calling time, subscription or extension groups (e.g. a virtual private network, VPN), user location services, and so on.
The present implementations of the intelligent network (IN) can comprise a service switching (or detection and triggering) point (SSP) and a service control point (SCP). These two points can also be in the form of an integrated unit or node (SSCP: service switching and control point). The detection and triggering arrangement can, for example, be such that the user dials a predefined telephone number including a predefined prefix indicating an IN call or then the entire number is used as IN call indicator. The switching point recognises the IN prefix or number and subsequently suspends the call handling and request further instruction from the control point. After having received the instructions from the control point the switching point will proceed accordingly. Subsequent to the triggering the control point controls the connection to the intelligent network and the various available functions thereof, depending on the intelligent network service in question. However, it is noted there are also various other possibilities than the above described for the detection and triggering (such as different timer arrangements).
The hitherto suggested MNP implementations are such that the user is allowed to retain his original MSISDN. Contrary to that, the IMSI (International Mobile Subscriber Identity) of the user must not be ported in the current applications, but the recipient network of the porting progress has to issue a new IMSI for the ported mobile subscription.
In operation, mobile telecommunication networks make several assumptions which are based on the MSISDN. Several procedures of mobile telecommunications networks, such as sorting and screening functions, are directly based on these assumptions. These assumptions essentially affect all the procedures that make use of the MSISDN number ranges or number spaces. The problem when using the number portability service is that many of these assumptions based on the MSISDN are no longer valid. For example, the MSISDN no longer indicates the actual subscription network (it gives only an indication of the original network), which has an affect on all such services which need the information of the actual network subscribed by the called party. In addition, the number ranges or spaces of the MSISDN can no longer be used in all mobile network functions (National Destination Code, for example).
One of the problems is caused by the fact that in case the call is made to a ported number, the intelligent network control point and thus the services behind the intelligent network control point will not become aware of the actual called number (B-number), i.e. the number in the actual network of the called subscriber. In addition, instances and applications where the mobile number portability services and the intelligent network services are used simultaneously have proven to be problematic. The use of ported numbers has also disadvantageous affects e.g. in relation with so called “home zone” type services or similar services where it is essential to know where the called subscriber is located at the time of the call and/or to which network/number range the called subscriber belongs (this affects e.g. the charging or the routing of the call or the service level provided for the call). This information could be obtained from a home location register of the subscribed networks, but if the called subscriber is a ported subscriber the supplementary telecommunications service is not aware of the address of the home location register for him. The use of the current type of routing registers also causes signalling load in the used networks and also within the intelligent network service. The routing of the calls to ported numbers is not always accomplished in an optimised manner as the calls are routed through the apparatus of the original (old) operator even in situations where neither the calling party or the called party is subscribing or using the original network.
These hitherto unsolved issues may have various kinds of affects in view of the controllability and management of the calls, e.g. in view of call charging, called user location data and back-signalling. Some of these affects may even be such that they may cause malfunction situations and/or excessive amount of signalling load in the network.